Recently, in a medical field, an X-ray image detection apparatus provided with a detection panel for converting X rays that have been transmitted through a human body into electrical signals and outputting the electrical signals as images instead of radiation films such as X-ray films has been in widespread use. As the detection panel, there are an indirect-conversion type detection panel and a direct-conversion type detection panel. In the indirect-conversion type detection panel, X rays are converted into visible light by phosphors, and the visible light is converted into electric charges by photoelectric conversion elements. In the direct-conversion type detection panel, the X rays are directly converted into electric charges by a photoconductor layer.
The detection panel is contained in a housing. To a surface of the housing at the side nearer to the X-ray generator is attached a surface plate made of carbon-based material having low X-ray absorptivity such as carbon fiber, so that the X rays are efficiently transmitted through the detection panel. On the surface plate are formed a square-frame shaped index as a first index showing a detection range of the detection panel, and a cross-shaped index as a second index showing a center position of the detection range of the detection panel, as disclosed in Japanese Patent Laid-Open Publication No. 2006-6424, for example. Alignment between the detection range of the detection panel and an irradiation field of the X-ray generator is performed using the first and second indices. Additionally, the first and second indices are used for positioning of a subject (human body), so that the subject to be imaged is included within the detection range.
In a radiographic image detection apparatus disclosed in Japanese Patent Laid-Open Publication No. 2006-6424, the indices are generally directly printed on the surface plate by using white color-based pigment whose main raw material is a metallic material such as white titanium. Therefore, as the metallic material contained in the pigment absorbs the radiation, the indices are unfavorably included in the radiographic image obtained by the detection panel. The inclusion of the indices gets in the way of interpretation of the radiographic image of a patient as the subject, and causes risk of the presence of an affected part being overlooked in a medical field.